Shades of Green: Electric Cars’ Carbon Emissions Around the Globe

The carbon emissions of grid powered electric cars in countries with coal based generation are no different to average petrol vehicles, while in countries with low carbon electricity they are less than half those of modern hybrids.

The scale of this variation implies that the climate benefits of going electric are not evenly shared around the globe.

The Carbon Emissions of Electric Cars

It is quite well understood that electric cars have the potential to reduce carbon emissions, but important to realize this potential is dependent on the type of electricity that charges the battery. Given that the vast majority of power generation around the world is grid-tied, where a car is charged plays a large role in determining its carbon emissions.

By considering the full scope of emissions that occur in both electricity supply and vehicle manufacturing this analysis compares the carbon emissions of electric cars in twenty of the world’s leading countries.

Electric cars’ carbon emissions can be four times greater in places with coal dominated generation than in those with low carbon power.

The legend to the right of this chart helps explain what is driving the variation between countries. All the difference between Paraguay and India is a result of changes in the fuel mix, from low carbon hydro at the bottom to high carbon coal at the top.

In India, Australia and China coal’s dominance in the fuel mix means that grid powered electric cars produce emissions ranging from 370-258 g CO2e/km, many multiples of those using low carbon sources.

Contrast this to hydroelectric exporter Paraguay where virtually all of the 70 g CO2e/km results from vehicle manufacturing, and electric driving is significantly lower carbon than using solar power.

Comparing Electric Emissions to Petrol Cars

Electric cars’ carbon emissions can vary from similar to average petrol cars to less than half those of the best petrol hybrids.

We show this by first accounting for the difference in vehicle manufacturing emissions and then calculating the equivalent petrol vehicle emissions in terms of fuel economy, MPGUS. Presented in this way the results are more intuitive, allowing us to compare electric car emissions with conventional vehicles in a more familiar metric.

The legend to the right gives a rough idea of which petrol vehicle, if any, has carbon emissions comparable to an electric vehicle in each country.

Based on data from 2009 the US petrol emissions equivalence is 40 MPGUS (9 L/100 km), similar to a modern petrol hybrid. But at the speed US electricity is decarbonizing this figure is rising quickly.

In the UK, Germany, Japan and Italy the broad fuel mix of natural gas, coal, nuclear and hydro means an electric vehicle’s carbon footprint is similar to the best comparable petrol hybrid, or most efficient diesel. In the UK this equals a petrol fuel economy of 44 MPGUS (5.4 L/100 km), while in Germany it rises to 47 MPGUS (5.0 L/100 km)

In Canada and France, where hydroelectricity and nuclear energy dominate, the petrol emission equivalences are 87 MPGUS (2.7 L/100 km) and 123 MPGUS (1.9 L/100 km) respectively. In these countries electric cars have the potential to more than halve total vehicle emissions.

Manufacturing Emissions Matter

As vehicles become increasing low carbon manufacturing emissions matter more and more.

Our central scenario for vehicle manufacturing was 70 g CO2e/km for an electric vehicle and 40 g CO2e/km for a petrol car. As explained in the report these estimates were made using the best available literature.

To highlight how important these assumptions are for low carbon vehicles we ran a crude sensitivity test by holding petrol manufacturing emissions constant while estimating a low (50 g CO2e/km) and high (90 g CO2e/km) scenario for electric vehicle manufacturing.

The results show that manufacturing emissions become increasingly important as electricity moves to low carbon sources.

At the bottom of the graph we can see that changing the manufacturing emissions assumptions does little to affect the equivalent emissions fuel economy. But as we reach countries like the US, UK and Germany the difference become significant. Finally at the top of the chart it has a very large effect.

Although we believe our central estimate of 70 g CO2e/km for electric vehicle manufacturing is a reasonable one, the more important point is to stress that in low carbon vehicles, whether hybrid, diesel, plug-in or full electric, manufacturing emissions are an important share of total emissions.

It requires much less refining than Petroleum so fuel production emissions should be lower. Small diesel engines can be upwards of 50% thermodynamically efficient compared to petrol’s 30% – the 1999 VW Lupo 3L and my own 2001 Audi A2 1.2 TDI (81 to 86g/km CO2 average) can achieve better than 3l/100km consumption. The latter has covered over 200,000 miles over 13 years without major overhaul – a petrol equivalent does not exist – if it did it would wear out more quickly as a diesel uses about half the RPM for the same cruise performance.

Modern Petrol emissions are now worse than diesels, not only in CO2 but some 10 times more particulates:

DEFRA calim UK grid mix is around 500g/kWh electricity. So what does that make a Leaf or BMW i3 CO2g/km in real world terms – I have driven the latter and managed just 80 mile range compared to my A2′s 330 miles.

What if WVO or Bio Diesel is used?

I still doubt that ethanol from Corn is a good idea given the low energy density cf petrol and increased corrosion issues in older petrol car fuel systems.